Microtomes are used for the production of thin sections of various specimens from medicine, biology, botany, and the materials research and quality control of technical materials, principally plastics. The production of these thin sections is effected using knives of various shapes and properties. Steel knives of selected tool steels are known, and are produced with various kinds of grinding. In addition to these regrindable knives, so-called disposable blades are widely used; for these, a distinction is principally made between so-called wide band blades and narrow band blades, which are replaced by new ones when their service life is exceeded. Furthermore, glass knives and diamond knives are used for special purposes.
Many knife carriers and holders for all kinds of knives are known in microtome technology; they additionally differ in their constitution according to the type of microtome they are provided for. These types are chiefly differentiated as rotary microtomes, in which the specimen is moved in the vertical direction towards a stationary knife, for section removal; slide microtomes, in which either the knife holder or the specimen holder is moved in a horizontal direction for section removal; and disk microtomes, in which the specimen is arranged on a disk which rotates relative to a stationary knife, for section removal. Microtomes which are used in microtome cryostats correspond to these types and differ solely by a rustproof embodiment.
The knife carriers and knife holders have the principal purpose of stably clamping the respective cutting tool, in order to attain the result of cutting in the form of a thin section of, for example, 3μ. In addition to a stable clamping, which prevents vibrations of the knife, most knife carriers and knife holders have devices for free angular adjustment between the knife edge and the specimen. Further features of typical knife carriers and knife holders are height adjustment devices for the knife to be clamped, clamp devices for fixing the knife carrier and knife holder on a microtome base plate or a microtome base frame, and also, in the case of knife carriers and knife holders for cryostatic microtomes, so-called section path devices. Knife carriers and knife holders are denoted hereinafter, for simplification, simply as knife holders.
When working with microtomes there always exists a danger of cuts to the hand from the microtome knife. Finger guards are therefore frequently provided, and have to be brought into their functional position, in which they cover the knife, in each working pause and in each preliminary operation of clamping the specimen in the specimen holder, or when adjusting the knife. In some known knife holders, the finger guard is arranged pivotably on the knife holder for this purpose. Other finger protection devices are not connected to the knife holder and can be set freely on the knife. In such cases they are frequently held in their position by means of weak magnets, or are positioned by pins. Furthermore, other finger protection devices consist of sideways displaceable rods or guard plates, which can be displaced so that they cover the middle cutting region of the knife edge during work pauses. These finger protection devices all have the disadvantage that they offer no protection during operation, that is, when a series of sections are cut on the microtome. Corresponding finger protection devices are described, for example, in U.S. Pat. No. 5,099,735 and GP patent 2,238,973.
A knife holder is described in U.S. Pat. No. 4,378,719 with covering elements for the cutting edge of the knife which are stationary relative to the knife. However, the covering elements only incompletely cover the blade. A knife holder with a section straightener, which likewise partially covers the blade, is described in U.S. Pat. No. 5,050,470.
Microtomes with knife holders are respectively described in U.S. Pat. No. 1,925,181 and U.S. Pat. No. 5,161,446, in which the above mentioned disadvantages are avoided. The finger protection devices described therein respectively have a cover plate for the knife edge, pivotably arranged on the base body of the knife holder, on the specimen side of the knife. When the specimen holder and the knife come close together, this cover plate is pivoted, by means of a driver cam, out of its functional position in which it covers the cutting edge of the knife, and thus first releases the cutting edge of the knife directly before the section removal. The cutting edge of the knife remains free, however, after a successful section removal, until the specimen holder has become separated again from the knife to such an extent that there is no longer any contact between the driver cam and the specimen holder. Therefore these protective devices cannot offer any effective protection from cutting injuries in this phase of the cutting process. Apart from this, the possibility also exists, when cutting specimens with relatively short dimensions in the direction of the cutting edge of the knife, of a finger inadvertently getting between the specimen and the knife blade when the cutting edge is already exposed, and thus suffering an injury.
It is therefore the object of the invention to provide a knife holder with a guard against cutting injuries which is also effective during the performance of cutting operations and section removal.